Microphonic transmitter.



No. 643,484. Patented Feb. I3, |90U.'

G. F. DUPONT.

(Application filed Apr. 1, 1898.]

(No Model.)

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UNITED STATES- PATENT OFFICE.

GEORGES FRANCOIS DUPONT, OF PARIS, FRANCE, ASSIGNOR TO PIERRE GERMAIN,OF EoNTENAY-AUxRosEs, FRANCE.

MICR'OPHONIC TRANSMITTER.

sPEc'IEIcA'rIoN forming part of Letters Patent No. 643,484, datedFebruary 13, 1906.

Application filed April 1, 1898. Serial No. 676,108. (No model.)

To all whom it may concern.-

Be it known that I, GEORGES FRANQOIS DU- 2 are views of a transmitterhaving a plural-',

ity of diaphragins, and Fig. 3 is an enlarged sectional view of one ofthe microphones shown in Fig. 2.

Referring to Fig. 1, the transmitter consists of two circular disks A A,of carbon baked or heated to 3,500 centigrade and providedwithpyramidical projections on the active or working surface a. These disksare electrically covered with metal over their outer or inactivesurfaces a". This operation should be eifected in such manner that thedeposited metal thoroughly enters or deeply penetrates into the carbonof the disks to reduce to a minimum their electrical resistance. Byusing carbon of suitable porosity this result is attained. A ring a isarranged around the two disks, and the space between the walls of thisring is subdivided by thin walls of mica or other insulating materialinto a number of cells a of equal surface, which are filled withgranulated carbon heated or baked at a very high temperature. Themicrophone is thus divided into a number of small similar microphonesbetween the two disks. In the type shown in the drawings there are eightcompartments.

While one of the disks, A, is secured to the ring a, the other, A, ismovable on its axis m 00. The movable disk is secured to a rigidaluminium cross a having four arms. These arms serve to secure on oneside four small spiral springs or, fixed to the other side by fouraluminium hooks fixed to or solid wit the ring and the disk A.

In the several cavities or recesses formed by the mica walls I place thesame quantity,

by volume and weight, of granulated carbon, the grains being of similarshape and size, and I provide springs of equal tension, so that themounting or setting up of the microphone 5 5 is effected without furtheradjustment.

I provide leading-in wires of refined copper twisted together andcovered with a coating of calcareous silicate base, which diminishes,metallic vibrations and retains indefinitely its properties in spite ofthe eventual action of heat. These wires are joined to the disks, eachof which has at the center a projecting cylindrical shoulder a". In themiddle of this shoulder is formed a hole into which is fixed a screw.One of these screws serves to connect the microphone to the vibratingmembrane B, which is thus the sole support of the disks and interposedgranulate.

By suitably regulating the microphonic cur- 7o rent a slight heatingtakes place within the mass of the granulate, which should scarcelyexceed 35 centigrade. This small amount of heat developed has adoubly-favorable effect without altering the properties of thesubstances forming the microphone. In the first place the activeresistance is reduced to a minimum with the minimum of dead-weight. Inthe second place the heatingremoves dampness, so harmful tomicrophoniceffects. To aid in this removal of dampness, small holes are formed inthe ring a. To maintain a perfect state of dryness of the airsurrounding the active granulate is so important that to thoroughlyeffect it I place in the compartment in which the microphone is mounteda small desiccating-tube. This tube can be of any desired shape. It canbe made of canvas or linen perforated in places andfilled with a finebeaten powder of absorbent cel 9o lulose and dry magnesium chlorid orwith any other similar substance. The proportion,by volume, of these twoproducts should be such that the Whole of the magnesium chlorid candeliquesce without a drop of liquid oozing 5 out of the perforated tube.

In the modification shown in Figs. 2, 2, and 3 the vibrating plate ofthe transmitter includes a certain number of similar diaphragms R ofspecial glass, having a thickness of from twelve to eighteen hundredthsof a millimeter and a diameter of from six to eight centi,-

meters. In front of each vibrating diaphragm is a rigid wall r, havingthe form of the hermetical cover, Fig. 2, or constituting an airchamberfurnished with a small opening 1", Fig. 3, for the escape of damp airand condensed water. The various air-chambers of the same apparatuscommunicate through tubes 8 with a single opening S, to which is securedthe mouthpiece.

In Fig. 3 I have shown an elastic tube of thin soft india-rubber t inplace of the mica ring of Fig. 1, and it has openings i Around therubber ring a light wire i is specially wound to close the openingssufliciently to prevent the fine granulate from passing out, without,however, reducing the elasticity of the whole.

The object of the subdivision of the microphone iuto a certain number ofsimilar and separate parts is to reduce the sparking due to excess involtage without necessitating undue compression of the gran ulate,whichwould greatly reduce the sensitiveness of the microare high currents,such as used in my system of microphone.

I may modify the details of construction of my improved microphonictransmitter without departing from the spirit of myinvention.

I claim as my invention- 1. A microphone consisting of carbon disks, aplurality of cells between them, granulated carbon in said cells andsprings adapted to hold the disks together, in combination with avibrating member, to which said disks are attached and by' which theyare solely carried, substantially as described.

2. A microphone consisting of a pair of carbon disks, elastic tubing ofless length than the diameter of the disks connecting said disks andgranulated carbon between them, in combination with springs to hold thedisks together and a vibrating membrane to which said disks are attachedand by which they are solely supported, substantially as described.

3. A microphone consisting of a pair of carbon disks, elastic tubingconnecting them, granulated carbon between them, openings in saidtubing, and wire around said tubing partially closing the openings toprevent the granulate from escaping, substantially as described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

GEORGES FRANCOIS DUPON".

Witnesses:

LEON FRANCKEN, EDWARD P. MAOLEAN.

